This invention relates to liquid dispensing apparatus and in particular to liquid dispensing apparatus which are able to dispense small volumes of liquid.
In certain applications it is desirable to be able to dispense very small volumes of liquid from a container, for example in the range 10-500 nanoliters (nl). Drops of this size cannot normally be produced by pumping liquid out of a capillary since surface tension will hold the drop to the tip of the capillary until it is sufficiently large that its weight overcomes this surface tension. This does not happen until the volume of the drop is of the order of 10 to 50 microliters—i.e. 2 to 3 orders of magnitude greater than the range of interest.
Devices are available which overcome this limitation by forcing a measured amount of liquid through the tip of a nozzle using a piezo-electric actuator acting on the liquid. However such systems are expensive and may only be used with a single type of liquid at a time—thus multiplying the cost where several different liquids need to be dispensed.